This invention relates to the purification of 2-chloro-1,1,1,2,3,3,3-heptafluoropropane (i.e., CF3CClFCF3 or CFC-217ba), its azeotropic compositions with hydrogen fluoride and their use in separation processes.
Hexafluoropropylene (i.e., CF3CFxe2x95x90CF2 or HFP), a valuable fluoromonomer can be prepared by the hydrodehalogenation of CF3CClFCF3 which itself can be prepared by the reaction of CF3CCl2CF3 (CFC-216aa) with HF (see e.g., U.S. Pat. Nos. 5,057,634 and 5,068,472). Typically excess HF is used to obtain favorable reaction rates for the conversion of CFC-216aa to CFC-217ba. HF may be removed from the halogenated hydrocarbon components of the product mixture using conventional aqueous solution scrubbing techniques. However, the production of substantial amounts of scrubbing discharge can create aqueous waste disposal concerns.
There remains a need for processes that utilize HF in such product mixtures in an environmentally benign manner.
This invention provides a process for the separation of a mixture comprising HF and CF3CClFCF3. The process comprises placing the mixture in a separation zone at a temperature of from about xe2x88x9230xc2x0 C. to about 100xc2x0 C. and at a pressure sufficient to maintain the mixture in the liquid phase, whereby an organic-enriched phase comprising less than 50 mole percent HF is formed as the bottom layer and an HF-enriched phase comprising more than 90 mole percent HF is formed as the top layer.
The organic-enriched phase can be withdrawn from the bottom of the separation zone and subjected to distillation in a distillation column to recover essentially pure CF3CClFCF3. The distillate comprising HF and CF3CClFCF3 can be removed from the top of the distillation column, while CF3CClFCF3 which is essentially free of HF can be recovered from the bottom of the distillation column. If desired, the distillate can be recycled to the separation zone.
The HF-enriched phase can be withdrawn from the top of the separation zone and subjected to distillation in a distillation column. The distillate comprising HF and CF3CClFCF3 can be removed from the top of the distillation column while essentially pure HF can be recovered from the bottom of the distillation column. If desired, the distillate can be recycled to the separation zone.
Also provided are compositions which comprise hydrogen fluoride in combination with an effective amount of CF3CClFCF3 to form an azeotrope or azeotrope-like composition with hydrogen fluoride, said composition containing from about 38.4 to 47.9 mole percent CF3CClFCF3.
Also provided is a process for producing 1,1,1,2,3,3,3-heptafluoropropane from a mixture comprising HF and CF3CClFCF3. The process is characterized by preparing CF3CClFCF3 which is essentially free of HF as indicated above, and reacting said CF3CClFCF3 with hydrogen.
Also provided is another process for producing 1,1,1,2,3,3,3-heptafluoropropane. This process is characterized by contacting an azeotrope of CF3CClFCF3 and HF as described above with hydrogen, and reacting the CF3CClFCF3 with hydrogen in the presence of HF.
Also provided is a process for producing hexafluoropropene from a mixture of comprising HF and CF3CClFCF3. The process is characterized by preparing CF3CClFCF3 which is essentially free of HF as indicated above, and dehalogenating the CF3CClFCF3.